1. Field of the Invention
The invention relates to a rolling bearing. More particularly, the invention relates to a rolling bearing that is used with grease lubrication under high speed of rotation.
2. Description of Related Art
Conventionally, a rolling bearing that is used in a machine, such as a turbo-molecular pump, which rotates at a high speed is generally lubricated with oil or oil mist. However, in recent years, grease is used as a lubricant because grease is easy to handle. In a case where grease is used as a lubricant, seal rings (sealing members) made of steel plates are arranged at end surface portions on the right and left sides of an annular space formed between an inner ring and an outer ring. Thus, outside leakage of the grease sealed inside the bearing is prevented.
However, when a rolling bearing having a conventional structure is used with grease lubrication under high speed of rotation, the grease sealed inside the bearing splashes to, for example, inner surfaces of seal rings due to centrifugal force in a relatively early stage. As a result, it becomes difficult to supply the lubricating oil content to raceways (at which rolling elements contact the inner peripheral surface of an outer ring and the outer peripheral surface of an inner ring, and which needs to be lubricated with a lubricant). Thus, vibrations and wear due to poor lubrication may easily occur within a short period of time.
Therefore, various measures for extending the retention time of the grease sealed inside the bearing have been suggested. For example, Japanese Patent Application Publication No. 2008-157441 JP-A-2008-157441) describes recessing the inner peripheral surface of an annular retainer 40 to form indentations 41 that serve as grease reservoirs, as shown in FIG. 3. There is a plurality of circular pockets 42 for retaining balls. Each of the indentations 41 is formed between the pockets 42 that are next to each other. In the retainer 40 described in JP-A-2008-157441, because the grease accumulates in the indentations 41 of the inner peripheral portion of the retainer 40, splash of the grease is prevented even if centrifugal force is high during high speed of rotation. Thus, the grease retention time is extended, and supply of the grease from the indentations 41 to ball surfaces lasts for a long period of time. As a result, it is possible to extend the operating service life of the bearing.
However, the indentations 41 of the retainer 40 described in JP-A-2008-157441 are recesses formed independently of the pockets 42 that accommodate the balls, that is, recesses formed so as not to be in communication with the pockets 42. Therefore, the grease is retained in the indentations 41 for a long period of time. However, there is a problem that it is difficult to smoothly supply the raceways with the oil content required for lubrication.